Concentrations are expressed as annual mean concentrations. Only complete series after inter/extrapolation are included (see indicator specification). The number of river stations/lake stations included per country is given in parenthesis.

Some countries measure nitrate plus nitrite (NO3 + NO2) = total Oxidized nitrogen - as nitrite (NO2) is usually a few percent of total Oxidized nitrogen, we have countries where nitrate is measured using a total of Oxidized Nitrogen